Heat exchanger and air conditioning system

ABSTRACT

A heat exchanger for exchanging heat under the ground or water includes an outer pipe ( 51 ) to be installed under the ground or water; and a cooling heat-transfer pipe ( 52 ) which is inserted into the outer pipe ( 51 ), and which dissipates heat from refrigerant injected thereto. A heat medium is sealed in the outer pipe ( 51 ). The outer pipe ( 51 ) and the cooling heat-transfer pipe ( 52 ) are arranged so that the liquid heat medium is held between an inner wall surface of the outer pipe ( 51 ) and an outer wall surface of the cooling heat-transfer pipe ( 52 ).

TECHNICAL FIELD

The present invention relates to a heat exchanger installed under theground or water, and an air conditioning system using the heatexchanger.

BACKGROUND ART

An example of a so-called “heat-pump heating system” which performsheating by a refrigeration cycle is a system in which ground heat orheat contained in water is used as a heat source to evaporaterefrigerant. For example, in a heat-pump heating system using groundheat, an underground heat exchanger for recovering ground heat from theground is used (see, e.g., Patent Document 1). In the heat exchanger ofPatent Document 1, a pipe (referred to as a “buried pipe” in thespecification) filled with a heat medium (secondary medium) is buriedunder the ground, and the heat medium inside the buried pipe isevaporated by ground heat. A pipe is branched from the buried pipe, andthen the heat exchanger is attached to the branched pipe. Heat recoveredin the heat exchanger is used as a heat source of the heat-pump heatingsystem.

CITATION LIST Patent Document

PATENT DOCUMENT 1: International Publication No. WO2004/111559

SUMMARY OF THE INVENTION Technical Problem

However, e.g., a conventional heat exchanger used under the ground isused only for heating, and cannot be used for both cooling and heating.Further, in, e.g., an underground heat exchanger extracting heat fromsoil, when using the compact underground heat exchanger, it is difficultto obtain a sufficient amount of heat with heat exchange capability ofthe conventional heat exchanger due to large heat transfer resistance ofthe soil. Thus, when an attempt is made to obtain a sufficient amount ofheat in, e.g., a so-called “vertical underground heat exchanger” buriedin the vertical direction, it is necessary to bury the underground heatexchanger to great depth. Specifically, there is an example in which aburial depth of approximately 100 m is required for an underground heatexchanger of a household heating system. Such a requirement of theburial depth of the underground heat exchanger causes a problem on itsinstallation cost. In a pipe, an area where working fluid is condensedis smaller than an area where the working fluid is evaporated, resultingin poor heat balance between the vaporization and the condensation.Although the condensed working fluid flows from an upper section of thepipe, a long wall surface of the pipe is not uniformly moistened. Thatis, the conventional underground heat exchanger does not effectivelyperform the heat exchange using ground heat.

In addition, in a broadly-used system in which water circulates insidethe underground heat exchanger to use heat from such circulating water,heat is indirectly exchanged through the water, thereby causing a lossin temperature gradient for such heat exchange. A tube line for runningwater into the pipe buried to the above-described depth, and a pump fortransferring the heat medium flowing in the tube are required, andtherefore there is a problem that power consumption of the pump degradesefficiency of the entire heating system. The foregoing problems may besimilarly caused when using the conventional underground heat exchangeras a condenser for cooling.

The present invention has been made in view of the foregoing problems,and it is an object of the present invention to improve heat exchangecapability in a heat exchanger arranged under the ground or water.

Solution to the Problems

In order to solve the foregoing problems, a first aspect of theinvention is intended for a heat exchanger including an outer pipe (51)to be installed under the ground or water; a cooling heat-transfer pipe(52) which is inserted into the outer pipe (51), and which dissipatesheat from refrigerant injected thereto; and a heat medium sealed in theouter pipe (51). In the heat exchanger, heat is dissipated by using achange in phase of the heat medium; and the outer pipe (51) and thecooling heat-transfer pipe (52) are arranged so that the liquid heatmedium is held between an inner wall surface of the outer pipe (51) andan outer wall surface of the cooling heat-transfer pipe (52).

Such a configuration allows the heat medium to be condensed byexchanging heat through the inner wall surface of the outer pipe (51)under the ground or water. The liquid heat medium is held through a heatmedium holding section (60) by surface tension, and therefore the outerwall surface of the cooling heat-transfer pipe (52) is uniformlymoistened by the liquid heat medium. Then, the cooling heat-transferpipe (52) exchanges heat with the condensed heat medium. Thus, the heatmedium is evaporated, and refrigerant inside the cooling heat-transferpipe (52) is condensed. The cooling heat-transfer pipe (52) exchangesheat under the ground or water by using the change in phase of the heatmedium. That is, the heat exchanger serves as a condenser.

A second aspect of the invention is intended for the heat exchanger ofthe first aspect of the invention, in which the cooling heat-transferpipe (52) contacts the inner wall surface of the outer pipe (51) forheat exchange.

This allows the direct heat exchange between the cooling heat-transferpipe (52) and the inner wall surface of the outer pipe (51).

A third aspect of the invention is intended for the heat exchanger ofthe first aspect of the invention, in which the cooling heat-transferpipe (52) extends from one end of the outer pipe (51) to the other end.

This allows the cooling heat-transfer pipe (52) to exchange heat withthe heat medium by using a broader area of the cooling heat-transferpipe (52).

A fourth aspect of the invention is intended for the heat exchanger ofthe first aspect of the invention, in which, in the outer pipe (51), awick (90) is provided along the inner wall surface of the outer pipe(51).

This allows the liquid heat medium inside the outer pipe (51) topenetrate the wick (90), and allows the wick (90) to held such heatmedium. In addition, the wick (90) allows the held liquid refrigerant tocontact the inner wall surface of the outer pipe (51).

A fifth aspect of the invention is intended for the heat exchange of thefirst aspect of the invention, in which grooves (100) for holding theheat medium by surface tension are formed in the inner wall surface ofthe outer pipe (51).

This allows the grooves (100) to held the liquid heat medium inside theouter pipe (51), and allows the held liquid refrigerant to contact theinner wall surface of the outer pipe (51).

A sixth aspect of the invention is intended for the heat exchanger ofthe first aspect of the invention, which further includes a heatingheat-transfer pipe (80) which is inserted into the outer pipe (51), andwhich evaporates refrigerant injected thereto.

Such a configuration allows the heat medium to be evaporated byexchanging heat through the inner wall surface of the outer pipe (51)under the ground or water during a heating operation. The heatingheat-transfer pipe (80) exchanges heat with the evaporated heat medium.Thus, the heat medium is condensed, and refrigerant inside the heatingheat-transfer pipe (80) is evaporated. That is, the heatingheat-transfer pipe (80) exchanges heat under the ground or water byusing the change in phase of the heat medium. This allows the heatingheat-transfer pipe (80) to serve as an evaporator for evaporatingrefrigerant, and therefore the heating heat-transfer pipe (80) absorbsheat from the ground or water.

A seventh aspect of the invention is intended for the heat exchanger ofthe first to sixth aspects of the invention, in which the coolingheat-transfer pipe (52) is formed in coiled shape.

This increases an area where the cooling heat-transfer pipe (52)contacts the heat medium.

An eighth aspect of the invention is intended for an air conditioningsystem including the heat exchanger of the first to seventh aspects ofthe invention to perform a refrigeration cycle.

This allows a cooling operation in which heat is dissipated to theground or water, or a heating operation in which heat contained in theground or water is used as a heat source, in the air conditioningsystem. In the cooling operation, the heat medium holding section (60)holds the liquid heat medium by the surface tension, and therefore theouter wall surface of the cooling heat-transfer pipe (52) is uniformlymoistened by the liquid heat medium. Consequently, vaporization isaccelerated.

ADVANTAGES OF THE INVENTION

According to the first aspect of the invention, the heat exchangerinstalled under the ground or water may be used for cooling. The outerwall surface of the cooling heat-transfer pipe (52) is uniformlymoistened by the liquid heat medium, and therefore heat is effectivelyexchanged between the outer wall surface of the cooling heat-transferpipe (52) and the liquid heat medium. Consequently, refrigerant insidethe cooling heat-transfer pipe (52) can be effectively condensed. Thatis, according to the present invention, heat exchange capability of theheat exchanger is improved, thereby allowing reduction in size of theheat exchanger.

According to the second aspect of the invention, heat is directlyexchanged between the cooling heat-transfer pipe (52) and the inner wallsurface of the outer pipe (51), and therefore refrigerant inside thecooling heat-transfer pipe (52) can be more effectively condensed.Consequently, the heat exchange capability of the heat exchanger isimproved.

According to the third aspect of the invention, the coolingheat-transfer pipe (52) exchanges heat with the heat medium by using thebroader area of the cooling heat-transfer pipe (52), thereby moreeffectively condensing refrigerant inside the cooling heat-transfer pipe(52). Consequently, the heat exchange capability of the heat exchangeris improved.

According to the fourth aspect of the invention, the liquid heat mediuminside the outer pipe (51) penetrates the wick (90), and is held by thewick (90). In addition, the wick (90) allows the held liquid refrigerantto contact the inner wall surface. Thus, uniform moistening of the innerwall surface of the outer pipe (51) can be ensured, thereby furtherimproving the heat exchange capability.

According to the fifth aspect of the invention, the grooves (100) holdthe liquid heat medium inside the outer pipe (51), and allow the heldliquid refrigerant to contact the inner wall surface of the outer pipe(51). Thus, the uniform moistening of the inner wall surface of theouter pipe (51) can be ensured, thereby further improving the heatexchange capability.

According to the sixth aspect of the invention, the heatingheat-transfer pipe (80) serves as the evaporator for evaporatingrefrigerant, and absorbs heat from the ground or water. Thus, the heatexchanger may be used as the condenser for cooling and the evaporatorfor heating.

According to the seventh aspect of the invention, the area where thecooling heat-transfer pipe (52) contacts the heat medium is increased.Thus, in the heat exchanger, heat exchange efficiency can be improved.

According to the eighth aspect of the invention, in the air conditioningsystem, the heat exchange capability of the heat exchanger isparticularly improved in the cooling operation. Such improvement of theheat exchanger capability allows the reduction in size of the heatexchanger, and may lead to reduction in cost of the air conditioningsystem.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system diagram of an air conditioning system including anunderground heat exchanger of a first embodiment.

FIG. 2 is a longitudinal sectional view illustrating a configuration ofthe underground heat exchanger of the first embodiment.

FIGS. 3(A) and 3(B) are views illustrating movement of refrigerant in acooling operation. FIG. 3(A) is a cross-sectional view of theunderground heat exchanger, and FIG. 3(B) is an enlarged view of a heatmedium holding section.

FIG. 4 is a system diagram of an air conditioning system including anunderground heat exchanger of a second embodiment.

FIG. 5 is a longitudinal sectional view illustrating a configuration ofthe underground heat exchanger of the second embodiment.

FIG. 6 is a view schematically illustrating a state in which anunderground heat exchanger (50) is installed so as to be inclined.

FIG. 7 is a view schematically illustrating a state in which anunderground heat exchanger (50) is horizontally installed.

FIG. 8 is a view schematically illustrating a state in which a heatexchanger (50) is installed under water.

FIGS. 9(A) and 9(B) are views illustrating an example of a configurationof an outer pipe. FIG. 9(A) is a cross-sectional view of the outer pipe,and FIG. 9(B) is a perspective view with a part of the outer pipe beingremoved.

FIG. 10 is a cross-sectional view further illustrating other example ofthe configuration of the outer pipe.

FIG. 11 is an example of a configuration of grooves (100), andillustrates the example in which the grooves (100) are formed in acircumferential direction.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described hereinafter withreference to the drawings. The embodiments below have been set forthmerely for purposes of preferred examples in nature, and are notintended to limit the scope, applications, and use of the invention. Inaddition, in the description of embodiments and variations below, thesame reference numeral is used throughout to refer to a component havingthe same function as that of a component which is first described, andthe description thereof will not be repeated.

First Embodiment of the Invention

In a first embodiment, an underground heat exchanger installed under theground will be described as an example of a heat exchanger of thepresent invention. The underground heat exchanger of the embodiments ofthe present invention is used for, e.g., a heat-pump air conditioningsystem which can perform a cooling operation. The underground heatexchanger serves as a condenser in the cooling operation, and dissipatesheat to soil.

Note that the “soil” includes layers containing only dirt, as well aswater-bearing layers containing both of dirt and water. That is,depending on a site and a depth of installation, the underground heatexchanger may exchange heat with dirt, water contained in the ground, orboth of them.

<Overall Configuration of Air Conditioning System>

FIG. 1 is a system diagram of an air conditioning system (1) includingan underground heat exchanger (50) of an embodiment of the presentinvention. As illustrated in FIG. 1, the air conditioning system (1) ofthe present embodiment includes a refrigerant circuit (10). A compressor(20), an indoor heat exchanger (30), an expansion valve (40), and theunderground heat exchanger (50) are connected to the refrigerant circuit(10). The refrigerant circuit (10) is filled with refrigerant (workingfluid).

The compressor (20) sucks refrigerant through a suction port to compresssuch refrigerant, and then discharges the compressed refrigerant througha discharge port. Specifically, various compressors such as a scrollcompressor may be employed as the compressor (20). In the refrigerantcircuit (10), the suction port of the compressor (20) is connected tothe indoor heat exchanger (30), and the discharge port of the compressor(20) is connected to the underground heat exchanger (50) (specifically,an entry section (52 a) which will be described later).

The indoor heat exchanger (30) is an air heat exchanger for exchangingheat between refrigerant and indoor air. In the air conditioning system(1), the indoor heat exchanger (30) is installed inside a so-called“indoor unit” arranged in a room to be air conditioned. In therefrigerant circuit (10), one end of the indoor heat exchanger (30) isconnected to the expansion valve (40), and the other end is connected tothe suction port of the compressor (20) as described above. In thecooling operation, heat contained in indoor air is absorbed bylow-pressure refrigerant flowing from the expansion valve (40) to theindoor heat exchanger (30). For example, a cross-fin type fin-and-tubeheat exchanger may be employed as the indoor heat exchanger (30). Anindoor fan (31) is installed near the indoor heat exchanger (30). Theindoor fan (31) sends air-conditioned air to the room.

An inflow hole of the expansion valve (40) is connected to theunderground heat exchanger (50) (specifically, an exit section (52 b)which will be described later). The expansion valve (40) expandsrefrigerant flowing from the underground heat exchanger (50) to reducethe pressure of such refrigerant to a predetermined pressure, and thendischarges the refrigerant to the indoor heat exchanger (30).

The underground heat exchanger (50) is buried under the ground, andexchanges heat with soil. Specifically, the underground heat exchanger(50) serves as a condenser in the cooling operation, and dissipates heatto soil. As illustrated in FIG. 2, the underground heat exchanger (50)of the present embodiment includes an outer pipe (51) and a coolingheat-transfer pipe (52).

The outer pipe (51) is formed in tubular shape with closed ends, and isvertically buried under the ground in this example. A geological layerincludes, e.g., a layer mainly containing dirt; a layer containing dirtand water; a layer mainly containing water; and a rock layer in whichrocks are successively distributed. The underground heat exchanger (50)may be installed in any of the geological layers.

A predetermined amount of carbon dioxide (CO₂) is sealed in the outerpipe (51) as a heat medium. As described later, the heat medium iscondensed by dissipating heat to soil through an inner wall surface ofthe outer pipe (51), and is evaporated by absorbing heat at an outerwall surface of the cooling heat-transfer pipe (52).

The cooling heat-transfer pipe (52) is formed in tubular shape, and isinserted into the outer pipe (51). In the refrigerant circuit (10),refrigerant is injected into the cooling heat-transfer pipe (52), andheat is dissipated from such refrigerant. Specifically, in therefrigerant circuit (10), one end of the cooling heat-transfer pipe (52)is connected to the discharge port of the compressor (20), and the otherend is connected to the expansion valve (40).

As illustrated in FIG. 2, the cooling heat-transfer pipe (52) of thepresent embodiment specifically includes the entry section (52 a), theexit section (52 b), an entry-side body section (52 c), an exit-sidebody section (52 d), and a connection section (52 e).

The entry section (52 a) is inserted into the outer pipe (51) from anupper side of the outer pipe (51) (a ground surface side in a state inwhich the outer pipe (51) is buried), and one end of the entry section(52 a) is connected to the discharge port of the compressor (20) througha pipe. The other end of the entry section (52 a) is connected to oneend of the entry-side body section (52 c) in an upper section inside theouter pipe (51). In addition, the exit section (52 b) is inserted intothe outer pipe (51) from the upper side of the outer pipe (51), and oneend of the exit section (52 b) outside the outer pipe (51) is connectedto the expansion valve (40) through a pipe. The other end of the exitsection (52 b) is connected to one end of the exit-side body section (52d) in the upper section inside the outer pipe (51).

Both of the entry-side body section (52 c) and the exit-side bodysection (52 d) extend from above the outer pipe (51) to a bottom sectionof the outer pipe (51) along the inner wall surface of the outer pipe(51). The connection section (52 e) crosses the bottom section in aradial direction, and one end of the entry-side body section (52 c) andone end of the exit-side body section (52 d) are connected together inthe bottom section.

The outer wall surface of the entry-side body section (52 c) and theinner wall surface of the outer pipe (51) define a heat medium holdingsection (60) for holding a liquid heat medium by surface tension.Similarly, the outer wall surface of the exit-side body section (52 d)and the inner wall surface of the outer pipe (51) also define a heatmedium holding section (60). Specifically, the outer wall surface of thebody section (52 c, 52 d) is arranged adjacent to the inner wall surfaceof the outer pipe (51). As illustrated in FIGS. 3(A) and 3(B), theliquid heat medium adhered on the inner wall surface of the outer pipe(51) is held between such walls (e.g., between the outer wall surface ofthe entry-side body section (52 c) and the inner wall surface of theouter pipe (51)) by the surface tension. As long as the liquid heatmedium can be held by the surface tension as described above, the outerwall surface of the body section (52 c, 52 d) does not necessarilycontact the inner wall surface of the outer pipe (51). However, in thepresent embodiment, the outer wall surfaces of the body sections (52 c,52 d) are arranged so as to contact the inner wall surface of the outerpipe (51). In this manner, the outer wall surfaces of the body sections(52 c, 52 d) are arranged so as to contact the inner wall surface of theouter pipe (51), thereby directly exchanging heat between the bodysection (52 c, 52 d) and the outer pipe (51). That is, such a directheat exchange improves heat exchange capability in the underground heatexchanger (50). In the underground heat exchanger (50), heat isexchanged by the two body sections which are the entry-side body section(52 c) and the exit-side body section (52 d). However, the number ofbody sections (52 c, 52 d) has been set forth merely for purposes ofexamples in nature, and it is not limited to the above.

Operation

Next, a process in the air conditioning system (1) during the coolingoperation will be described.

When staring the cooling operation, if the compressor (20) comes intooperation, then compressed refrigerant (gaseous refrigerant) isdischarged through the discharge port of the compressor (20). Therefrigerant discharged from the compressor (20) is sent to the entrysection (52 a) of the underground heat exchanger (50), and is furtherinjected into the body sections (52 c, 52 d).

In such a state, the inner wall surface of the outer pipe (51) initiallyhas a temperature equal to the ground temperature. After a predeterminedperiod of time is elapsed from such a point, the temperature increasesin the body sections (52 c, 52 d) due to large heat transfer resistanceof soil. An amount of heat to be transferred between the outer pipe (51)and soil is limited by the heat transfer resistance of soil. Thus, aflow rate of refrigerant is generally controlled so that heat istransferred within a range in which a temperature gradient between theinner wall surface of the outer pipe (51) and the body section (52 c, 52d) is maintained, and in which a temperature distribution under theground is maintained constant. Meanwhile, a part of the heat medium iscondensed to liquid by dissipating heat to soil through the inner wallsurface of the outer pipe (51). This functions to avoid concentration ofthe heat transfer in sections where the inner wall surface of the outerpipe (51) contacts the body sections (52 c, 52 d), and to dissipate anddisperse heat across the entire inner wall surface of the outer pipe(51). As illustrated in FIG. 3, the liquid heat medium is attracted tothe heat medium holding section (60) defined between the inner wallsurface of the outer pipe (51) and the outer wall surface of the bodysection (52 c, 52 d), by the surface tension caused in the heat mediumholding section (60). The heat medium condensed in the outer pipe (51)is attracted to the outer wall surface of the body section (52 c, 52 d)through the heat medium holding section (60), and therefore the outerwall surface of the body section (52 c, 52 d) is uniformly moistened bythe liquid heat medium. The heat medium on the outer wall surface of thebody section (52 c, 52 d) is evaporated by absorbing heat from the bodysection (52 c, 52 d). The heat medium evaporated in this manner isrecondensed by dissipating heat to soil through the inner wall surfaceof the outer pipe (51).

Meanwhile, the body section (52 c, 52 d) dissipates heat to the heatmedium contacting the body section (52 c, 52 d), and then furtherdissipates such heat to soil through the inner wall surface of the outerpipe (51), which contacts the body section (52 c, 52 d). The bodysection (52 c, 52 d) dissipates heat in this manner, thereby condensingrefrigerant injected into the body section (52 c, 52 d). The condensedrefrigerant is injected into the expansion valve (40) through the exitsection (52 b). Subsequently, the pressure of the refrigerant is reducedby the expansion valve (40), and then such refrigerant is injected intothe indoor heat exchanger (30). The refrigerant flowing into the indoorheat exchanger (30) is evaporated by absorbing heat from indoor air.This cools the indoor air in the indoor heat exchanger (30), and thecooled indoor air is sent back to the room by the indoor fan (31). Therefrigerant evaporated in the indoor heat exchanger (30) is injectedinto the compressor (20) through the suction port. The compressor (20)sucks and compresses such refrigerant to discharge it to the entrysection (52 a) of the underground heat exchanger (50). As describedabove, in the underground heat exchanger (50), the cooling heat-transferpipe (52) exchanges heat with soil by using a change in phase of theheat medium.

In the air conditioning system (1), the above-described process isrepeated, and therefore a refrigeration cycle (in this example, thecooling operation) is performed, in which the underground heat exchanger(50) serves as the condenser to compress refrigerant in the compressor(20).

As described above, in the present embodiment, the heat medium condensedin the outer pipe (51) is attracted to the outer wall surface of thebody section (52 c, 52 d) of the cooling heat-transfer pipe (52) throughthe heat medium holding section (60), and therefore the outer wallsurface of the body section (52 c, 52 d) is uniformly moistened by theliquid heat medium. Thus, heat is effectively exchanged between theouter wall surface of the body section (52 c, 52 d) and the liquid heatmedium, thereby effectively condensing refrigerant in the coolingheat-transfer pipe (52). That is, in the present embodiment, the heatexchange capability of the underground heat exchanger is improved,thereby allowing reduction in size of the underground heat exchanger.Such size reduction may lead to reduction in cost of the airconditioning system.

Second Embodiment of the Invention

In a second embodiment, an air conditioning system which allows aheating operation in addition to a cooling operation will be described.

FIG. 4 is a system diagram of an air conditioning system (2) includingan underground heat exchanger (50) of the second embodiment. Asillustrated in FIG. 4, the air conditioning system (2) includes arefrigerant circuit (70). The refrigerant circuit (70) is configured byadding a four-way reversing valve (71), a first switching valve (72),and a second switching valve (73) to the refrigerant circuit (10) of thefirst embodiment.

The four-way reversing valve (71) includes first to fourth ports. Thefour-way reversing valve (71) is switchable between a first state inwhich the first port communicates with the third port, and the secondport communicates with the fourth port (a state indicated by a solidline in FIG. 4); and a second state in which the first port communicateswith the fourth port, and the second port communicates with the thirdport (a state indicated by a dashed line in FIG. 4). In the refrigerantcircuit (70), the first port is connected to a discharge port of acompressor (20), and the second port is connected to a suction port ofthe compressor (20). In addition, the third port is connected to thesecond switching valve (73), and the fourth port is connected to one endof an indoor heat exchanger (30).

As illustrated in FIG. 5, the underground heat exchanger (50) of thepresent embodiment is configured by adding a heating heat-transfer pipe(80) to the underground heat exchanger (50) of the first embodiment.

The heating heat-transfer pipe (80) includes an entry section (80 a), abody section (80 b), and an exit section (80 c). In the body section (80b), injected refrigerant is evaporated by absorbing heat from a heatmedium in the heating operation. In the present embodiment, the bodysection (80 b) is formed in coiled shape, and is arranged so as tosurround an entry section (52 a) and an exit section (52 b) of a coolingheat-transfer pipe (52) in an upper section inside an outer pipe (51).The entry section (80 a) is a pipe for injecting refrigerant into thebody section (80 b), and the exit section (80 c) is a pipe for ejectingrefrigerant from the body section (80 b). In the present embodiment,both of the entry section (80 a) and the exit section (80 c) are formedso as to be straight, and are inserted into the outer pipe (51) fromabove.

The first and second switching valves (72, 73) are valves for switchinga flow of refrigerant depending on whether the heating or coolingoperation is performed in the air conditioning system (2). The firstswitching valve (72) connects an expansion valve (40) to either one ofthe exit section (52 b) of the cooling heat-transfer pipe (52) and theentry section (80 a) of the heating heat-transfer pipe (80). Inaddition, the second switching valve (73) connects the third port of thefour-way reversing valve (71) to either one of the entry section (52 a)of the cooling heat-transfer pipe (52) and the exit section (80 c) ofthe heating heat-transfer pipe (80).

Operation

Next, an operation in the air conditioning system (2) will be described.

(Cooling Operation)

First, the cooling operation will be described. In the coolingoperation, the four-way reversing valve (71) is switched to the firststate. That is, the first port communicates with the third port, and thesecond port communicates with the fourth port (the state indicated bythe solid line in FIG. 4). In addition, the first switching valve (72)is switched so that the expansion valve (40) and the exit section (52 b)of the cooling heat-transfer pipe (52) are connected together, and thesecond switching valve (73) is switched so that the entry section (52 a)of the cooling heat-transfer pipe (52) and the third port of thefour-way reversing valve (71) are connected together. This allows therefrigerant circuit (70) to be equivalent to the refrigerant circuit(10) of the first embodiment. Thus, the same operation as that of theair conditioning system (1) of the first embodiment is performed in theair conditioning system (2), and a refrigeration cycle (in this example,the cooling operation) is performed, in which the underground heatexchanger (50) serves as a condenser to compress refrigerant in thecompressor (20).

(Heating Operation)

Next, the heating operation of the air conditioning system (2) will bedescribed. In the heating operation, the four-way reversing valve (71)is switched to the second state. That is, the first port communicateswith the fourth port, and the second port communicates with the thirdport (the state indicated by the dashed line in FIG. 4). In addition,the first switching valve (72) is switched so that the expansion valve(40) and the entry section (80 a) of the heating heat-transfer pipe (80)are connected together, and the second switching valve (73) is switchedso that the exit section (80 c) of the heating heat-transfer pipe (80)and the third port of the four-way reversing valve (71) are connectedtogether.

In such a state, when the compressor (20) comes into operation,compressed refrigerant (gaseous refrigerant) is discharged through thedischarge port of the compressor (20). Subsequently, the refrigerantdischarged from the compressor (20) is sent to the indoor heat exchanger(30) through the four-way reversing valve (71). The refrigerant flowinginto the indoor heat exchanger (30) dissipates heat to room air in theindoor heat exchanger (30). The room air is heated in the indoor heatexchanger (30), and the heated room air is sent back to a room by anindoor fan (31). The refrigerant dissipating heat in the indoor heatexchanger (30) is sent to the expansion valve (40). The pressure of therefrigerant flowing into the expansion valve (40) is reduced whenpassing through the expansion valve (40). Subsequently, such refrigerantflows into the entry section (80 a) of the heating heat-transfer pipe(80), and then is injected into the body section (80 b).

In such a state, an inner wall surface of the outer pipe (51) initiallyhas a temperature equal to the ground temperature. However, due to largeheat transfer resistance, a temperature gradient proportional to anamount of heat dissipated to the heating heat-transfer pipe (80) throughthe heat medium is generated, thereby decreasing the temperature ofsoil. Heat transport is controlled so that heat is transferred within arange in which the temperature gradient between the inner wall surfaceof the outer pipe (51) and the heating heat-transfer pipe (80) ismaintained, and in which a temperature distribution under the ground ismaintained constant. A part of the heat medium is evaporated into gas byabsorbing heat from soil through the inner wall surface of the outerpipe (51). Heat is absorbed from such gaseous heat medium by the bodysection (80 b) of the heating heat-transfer pipe (80), and then the heatmedium is condensed to liquid. The liquid heat medium is evaporated byreabsorbing heat from soil through the inner wall surface.

Meanwhile, in the body section (80 b), the body section (80 b) absorbsheat from the heat medium, and therefore injected refrigerant isevaporated and changed into gas refrigerant. The gas refrigerant isejected from the exit section (80 c) of the heating heat-transfer pipe(80), and then is injected to the suction port of the compressor (20)through the second switching valve (73) and the four-way reversing valve(71). The compressor (20) sucks and compresses such refrigerant, andthen discharges the refrigerant to the indoor heat exchanger (30)through the four-way reversing valve (71). In the air conditioningsystem (2), the above-described process is repeated to perform arefrigeration cycle (in this example, the heating operation) in whichthe underground heat exchanger (50) serves as an evaporator to compressrefrigerant in the compressor (20).

Variation of First and Second Embodiments

The underground heat exchanger (50) of the first and second embodimentsmay be installed so as to be inclined in a direction other than thelongitudinal direction. FIG. 6 is a view schematically illustrating astate in which an underground heat exchanger (50) is installed so as tobe inclined. Even in such installation, heat is exchanged as in each ofthe embodiments. In FIG. 6, the “HP” represents a body section (sectionother than a heat exchanger) of an air conditioning system (1) (or anair conditioning system (2)) (hereinafter, the same reference characteris used to refer to the same component).

Third Embodiment of the Invention

The underground heat exchanger (50) of the first embodiment may behorizontally installed. An underground heat exchanger (50) of thepresent embodiment is used for a cooling operation. FIG. 7 is a viewschematically illustrating a state in which the underground heatexchanger (50) is horizontally installed. A geological layer includes,e.g., a layer mainly containing dirt; a layer containing dirt and water;a layer mainly containing water; and a rock layer in which rocks aresuccessively distributed. The underground heat exchanger (50) may beinstalled in any of the geological layers, or may be installed so as tocross a plurality of layers. In FIG. 7, a first example illustrates anexample in which the underground heat exchanger (50) is installed in thelayer mainly containing dirt; a second example illustrates an example inwhich the underground heat exchanger (50) is installed in the layercontaining dirt and water; a third example illustrates an example inwhich the underground heat exchanger (50) is installed in the layermainly containing water; and a fourth example illustrates an example inwhich the underground heat exchanger (50) is installed in the rocklayer.

Fourth Embodiment of the Invention

The heat exchanger of the foregoing embodiments and the variation may beinstalled under the ground, as well as under water. An installation sitespecifically includes, e.g., the sea, a lake, a pond, a pool, a waterstorage tank, a river, and a sewage system. FIG. 8 is a viewschematically illustrating a state in which a heat exchanger (50) isinstalled under water. In this figure, five examples (first to fifthexamples) are illustrated as examples of installation of the heatexchanger (50) (underwater heat exchanger). The first and secondexamples are examples in which the heat exchanger (50) is installed inthe water storage tank or the pool. In the first example, the heatexchanger (50) is vertically arranged; and, in the second example, theheat exchanger (50) is horizontally arranged. The third and fourthexamples are examples in which the heat exchanger (50) is installed inthe sea, a lake, or a pond. In the third example, the heat exchanger(50) is vertically arranged; and, in the fourth example, the heatexchanger (50) is horizontally arranged. The fifth example is an examplein which the heat exchanger (50) is installed in the sewage system, andis horizontally arranged. That is, when installing the heat exchanger(50) under water, the heat exchanger (50) may be vertically orhorizontally arranged. In addition, when installing the heat exchanger(50) under water, the heat exchanger (50) may be installed so as to beinclined (see an sixth example in FIG. 8).

When installing the heat exchanger (50) under water as described above,heat is exchanged by the same mechanism as those of the foregoingembodiments and the variation.

Other Embodiments (Variations) <1> As illustrated in FIGS. 9(A) and9(B), a wick (90) may be provided on an inner wall surface of an outerpipe (51). A liquid heat medium inside the outer pipe (51) penetratesthe wick (90), and is held by the wick (90). The wick (90) allows theheld liquid refrigerant to contact the inner wall surface of the outerpipe (51). The wick (90) includes, e.g., an assembly of a porous metalbody, porous ceramic, and fibers. The wick (90) is provided on the innerwall surface of the outer pipe (51) as described above, thereby ensuringuniform moistening of the inner wall surface of the outer pipe (51).Consequently, heat exchange capability is improved particularly in aheating operation.

<2> As illustrated in a cross-sectional view of FIG. 10, a plurality ofgrooves (100) may be provided in an inner wall surface of an outer pipe(51). Specifically, the width, depth, and number of the grooves (100)are set so that a liquid heat medium inside the outer pipe (51) is held.A direction of the grooves (100) is not limited to a direction parallelto an axial direction of the outer pipe (51). For example, the grooves(100) may be formed in a circumferential direction, or may be helicallyformed. The grooves (100) are provided in the inner wall surface of theouter pipe (51), thereby ensuring uniform moistening of the inner wallsurface of the outer pipe (51). Consequently, heat exchange capabilityis improved particularly in a heating operation. For example, FIG. 11illustrates an example of the outer pipe (51) in which the grooves (100)are formed in the circumferential direction. For example, when anunderground heat exchanger (50) is horizontally installed, the grooves(100) are formed in the circumferential direction as described above,thereby more effectively ensuring the uniform moistening of the innerwall surface of the outer pipe (51).

-   -   <3> A heating heat-transfer pipe (80) is not limited to the        above as long as the heating heat-transfer pipe (80) serves as a        heat exchanger for heating (evaporator).    -   <4> In the foregoing embodiments, a cooling heat-transfer pipe        (52) may be formed in coiled shape. This increases an area where        the cooling heat-transfer pipe (52) contacts the heat medium.        Thus, in the heat exchanger, heat exchange efficiency can be        improved.    -   <5> In any of the embodiments and the variations, a plurality of        heat exchangers (50) may be installed.

INDUSTRIAL APPLICABILITY

The present invention is useful for the heat exchanger installed underthe ground or water, and the air conditioning system using the heatexchanger.

DESCRIPTION OF REFERENCE CHARACTERS

-   1, 2 Air Conditioning System-   50 Underground Heat Exchanger (Heat Exchanger)-   51 Outer Pipe-   52 Cooling Heat-Transfer Pipe-   60 Heat Medium Holding Section-   80 Heating Heat-Transfer Pipe-   90 Wick-   100 Groove

1. A heat exchanger, comprising: an outer pipe (51) to be installedunder the ground or water; a cooling heat-transfer pipe (52) which isinserted into the outer pipe (51), and which dissipates heat fromrefrigerant injected thereto; and a heat medium sealed in the outer pipe(51), wherein heat is dissipated by using a change in phase of the heatmedium; the outer pipe (51) and the cooling heat-transfer pipe (52) arearranged so that the liquid heat medium is held between an inner wallsurface of the outer pipe (51) and an outer wall surface of the coolingheat-transfer pipe (52).
 2. The heat exchanger of claim 1, wherein thecooling heat-transfer pipe (52) contacts the inner wall surface of theouter pipe (51) for heat exchange.
 3. The heat exchanger of claim 1,wherein the cooling heat-transfer pipe (52) extends from one end of theouter pipe (51) to the other end.
 4. The heat exchanger of claim 1,wherein, in the outer pipe (51), a wick (90) is provided along the innerwall surface of the outer pipe (51).
 5. The heat exchanger of claim 1,wherein grooves (100) for holding the heat medium by surface tension areformed in the inner wall surface of the outer pipe (51).
 6. The heatexchanger of claim 1, further comprising: a heating heat-transfer pipe(80) which is inserted into the outer pipe (51), and which evaporatesrefrigerant injected thereto.
 7. The heat exchanger of claim 1, whereinthe cooling heat-transfer pipe (52) is formed in coiled shape.
 8. An airconditioning system, comprising: the heat exchanger of claim 1 toperform a refrigeration cycle.